1. Field of the Invention
The present invention relates to electrical connectors, especially to ball grid array (BGA) connectors having a plurality of solder balls for surface mount to printed circuit boards.
2. Background of the Invention
Various types of conventional electrical connectors are known for electrically connecting a chip package, such as a CPU, with a circuit board, such as a printed circuit board.
One of the widely-known and used-friendly electrical connectors is a BGA connector, particularly utilized for electrically connecting the chip package with the PCB. The BGA connector generally has a base housing defining a central hole surrounded by a plurality of passageways arranged in a matrix. A plurality of terminals are inserted into the passageways, and have first ends thereof connected to the printed circuit board via an array of solder balls extending from a bottom surface of the housing, and second opposite ends connected to conductive elements of the chip package mounted on the housing. Typically, the conductive elements are in form of land grid array serving as electrodes for connecting the terminals on the base housing. With the current chip package, such as a CPU, to be required operating at higher speeds, the number of lands is extremely large, and thus connection resistance between the lands and the terminals is very great.
There are several solutions developed to overcome this problem. One of the solutions is provided with a power assistance mechanism including a stiffener, a lever, a clip and etc. The stiffener generally defines an opening to grasp a periphery of the housing. The clip and the lever respectively disposed at two ends of the stiffener or the housing to jointly press the CPU chip onto the housing to make electrically connection between the lands of the CPU chip and the terminals on the base housing.
Since the power assistance mechanism is mainly made of metal and may have a dissymmetrical configuration, particularly due to the lever, which contribute to the weight of the power assistance mechanism, the center of gravity of the BGA connector tends to be at a position biased toward the lever side or a heavier connector end portion, as opposed to a center of the array of solder balls of the terminals that are soldered to the printed circuit board.
Due to the positional misalignment between the center of the array of solder balls and the center of gravity of the BGA connector, during reflow soldering of the BGA connector to the printed circuit board, the heavier connector end portion or the lever side is caused to rotate toward the printed circuit board, thereby causing the lighter connector end portion on the opposite side to be separated from the printed circuit board. Thus, the BGA connector may be mounted on the printed circuit board at an inclination, thereby causing electrical connection failure.